Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifier AD8628/AD8629 Automotive sensors Pressure and position sensors Strain gage amplifiers Medical instrumentation Thermocouple amplifiers Precision current sensing Photodiode amplifier V– 2 AD8628 5 V+ 4 –IN TOP VIEW (Not to Scale) +IN 3 02735-001 OUT 1 Figure 1. 5-Lead TSOT (UJ-5) and 5-Lead SOT-23 (RT-5) NC 1 –IN 2 AD8628 +IN 3 TOP VIEW V– 4 (Not to Scale) 8 NC 7 V+ 6 OUT 5 NC NC = NO CONNECT 02735-002 APPLICATIONS PIN CONFIGURATIONS Figure 2. 8-Lead SOIC (R-8) OUT A 1 –IN A 2 AD8629 8 V+ 7 OUT B +IN A 3 6 –IN B TOP VIEW V– 4 (Not to Scale) 5 +IN B 02735-063 Lowest auto-zero amplifier noise Low offset voltage: 1 µV Input offset drift: 0.002 µV/°C Rail-to-rail input and output swing 5 V single-supply operation High gain, CMRR, and PSRR: 120 dB Very low input bias current: 100 pA max Low supply current: 1.0 mA Overload recovery time: 10 µs No external components required Figure 3. 8-Lead SOIC (R-8) OUT A 1 –IN A 2 AD8629 +IN A 3 TOP VIEW (Not to Scale) V– 4 8 V+ 7 OUT B 6 –IN B 5 +IN B 02735-064 FEATURES Figure 4. 8-Lead MSOP (RM-8) GENERAL DESCRIPTION This new breed of amplifier has ultralow offset, drift, and bias current. The AD8628/AD8629 are wide bandwidth auto-zero amplifiers featuring rail-to-rail input and output swings and low noise. Operation is fully specified from 2.7 V to 5 V single supply (±1.35 V to ±2.5 V dual supply). The AD8628/AD8629 provide benefits previously found only in expensive auto-zeroing or chopper-stabilized amplifiers. Using Analog Devices’ new topology, these zero-drift amplifiers combine low cost with high accuracy and low noise. (No external capacitor is required.) In addition, the AD8628/AD8629 greatly reduce the digital switching noise found in most chopper-stabilized amplifiers. With an offset voltage of only 1 µV, drift of less than 0.005 µV/°C, and noise of only 0.5 µV p-p (0 Hz to 10 Hz), the AD8628/AD8629 are perfectly suited for applications in which error sources cannot be tolerated. Position and pressure sensors, medical equipment, and strain gage amplifiers benefit greatly from nearly zero drift over their operating temperature range. Many systems can take advantage of the rail-to-rail input and output swings provided by the AD8628/AD8629 to reduce input biasing complexity and maximize SNR. The AD8628/AD8629 are specified for the extended industrial temperature range (−40°C to +125°C). The AD8628 is available in tiny TSOT-23, SOT-23, and the popular 8-lead narrow SOIC plastic packages. The AD8629 is available in the standard 8-lead narrow SOIC and MSOP plastic packages. Rev. C Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.326.8703 © 2004 Analog Devices, Inc. All rights reserved. AD8628/AD8629 TABLE OF CONTENTS Specifications..................................................................................... 3 Total Integrated Input-Referred Noise for First-Order Filter15 Electrical Characteristics ............................................................. 3 Input Overvoltage Protection ................................................... 16 Absolute Maximum Ratings............................................................ 5 Output Phase Reversal............................................................... 16 ESD Caution.................................................................................. 5 Overload Recovery Time .......................................................... 16 Typical Performance Characteristics ............................................. 6 Infrared Sensors.......................................................................... 17 Functional Description .................................................................. 14 Precision Current Shunts .......................................................... 18 1/f Noise....................................................................................... 14 Output Amplifier for High Precision DACs ........................... 18 Peak-to-Peak Noise .................................................................... 15 Outline Dimensions ....................................................................... 19 Noise Behavior with First-Order Low-Pass Filter.................. 15 Ordering Guide .......................................................................... 20 REVISION HISTORY 10/04—Data Sheet Changed from Rev. B to Rev. C Updated Formatting ...........................................................Universal Added AD8629....................................................................Universal Added SOIC and MSOP Pin Configurations ............................... 1 Added Figure 48.............................................................................. 13 Changes to Figure 62...................................................................... 17 Added MSOP Package ................................................................... 19 Changes to Ordering Guide .......................................................... 20 10/03—Data Sheet Changed from Rev. A to Rev. B Changes to General Description .................................................... 1 Changes to Absolute Maximum Ratings ....................................... 4 Changes to Ordering Guide ............................................................ 4 Added TSOT-23 Package............................................................... 15 6/03—Data Sheet Changed from Rev. 0 to Rev. A Changes to Specifications ................................................................ 3 Changes to Ordering Guide ............................................................ 4 Change to Functional Description ............................................... 10 Updated Outline Dimensions ....................................................... 15 10/02—Revision 0: Initial Version Rev. C | Page 2 of 20 AD8628/AD8629 SPECIFICATIONS ELECTRICAL CHARACTERISTICS VS = 5.0 V, VCM = 2.5 V, TA = 25°C, unless otherwise noted. Table 1. Parameter INPUT CHARACTERISTICS Offset Voltage Symbol Conditions Min VOS Typ Max Unit 1 5 10 100 1.5 200 250 5 µV µV pA nA pA pA V dB dB dB dB µV/°C −40°C ≤ TA ≤ +125°C Input Bias Current IB 30 −40°C ≤ TA ≤ +125°C Input Offset Current IOS 50 −40°C ≤ TA ≤ +125°C Input Voltage Range Common-Mode Rejection Ratio CMRR Large Signal Voltage Gain1 AVO Offset Voltage Drift OUTPUT CHARACTERISTICS Output Voltage High ∆VOS/∆T VOH Output Voltage Low VOL Short-Circuit Limit ISC VCM = 0 V to 5 V −40°C ≤ TA ≤ +125°C RL = 10 kΩ, VO = 0.3 V to 4.7 V −40°C ≤ TA ≤ +125°C −40°C ≤ TA ≤ +125°C RL = 100 kΩ to ground −40°C ≤ TA ≤ +125°C RL = 10 kΩ to ground −40°C ≤ TA ≤ +125°C RL = 100 kΩ to V+ −40°C ≤ TA ≤ +125°C RL = 10 kΩ to V+ −40°C ≤ TA ≤ +125°C 0 120 115 125 120 4.99 4.99 4.95 4.95 ±25 −40°C ≤ TA ≤ +125°C Output Current IO −40°C ≤ TA ≤ +125°C POWER SUPPLY Power Supply Rejection Ratio Supply Current/Amplifier INPUT CAPACITANCE Differential Common-Mode DYNAMIC PERFORMANCE Slew Rate Overload Recovery Time Gain Bandwidth Product NOISE PERFORMANCE Voltage Noise Voltage Noise Density Current Noise Density 1 PSRR ISY VS = 2.7 V to 5.5 V −40°C ≤ TA ≤ +125°C VO = 0 V −40°C ≤ TA ≤ +125°C CIN SR 4.996 4.995 4.98 4.97 1 2 10 15 ±50 ±40 ±30 ±15 130 0.85 1.0 0.02 5 5 20 20 1.1 1.2 V V V V mV mV mV mV mA mA mA mA dB mA mA 1.5 10 pF pF RL = 10 kΩ 1.0 0.05 2.5 V/µs ms MHz 0.1 Hz to 10 Hz 0.1 Hz to 1.0 Hz f = 1 kHz f = 10 Hz 0.5 0.16 22 5 µV p-p mV p-p nV/√Hz fA/√Hz GBP en p-p en p-p en in 115 140 130 145 135 0.002 Gain testing is highly dependent upon test bandwidth. Rev. C | Page 3 of 20 AD8628/AD8629 VS = 2.7 V, VCM = 1.35 V, VO = 1.4 V, TA = 25°C, unless otherwise noted. Table 2. Parameter INPUT CHARACTERISTICS Offset Voltage Symbol Conditions Min VOS Typ Max Unit 1 5 10 100 1.5 200 250 5 µV µV pA nA pA pA V dB dB dB dB µV/°C −40°C ≤ TA ≤ +125°C Input Bias Current IB 30 1.0 50 −40°C ≤ TA ≤ +125°C Input Offset Current IOS −40°C ≤ TA ≤ +125°C Input Voltage Range Common-Mode Rejection Ratio CMRR Large Signal Voltage Gain AVO Offset Voltage Drift OUTPUT CHARACTERISTICS Output Voltage High ∆VOS/∆T VOH Output Voltage Low VOL Short-Circuit Limit ISC VCM = 0 V to 2.7 V −40°C ≤ TA ≤ +125°C RL = 10 kΩ , VO = 0.3 V to 2.4 V −40°C ≤ TA ≤ +125°C −40°C ≤ TA ≤ +125°C RL = 100 kΩ to ground −40°C ≤ TA ≤ +125°C RL = 10 kΩ to ground −40°C ≤ TA ≤ +125°C RL = 100 kΩ to V+ −40°C ≤ TA ≤ +125°C RL = 10 kΩ to V+ −40°C ≤ TA ≤ +125°C 0 115 110 110 105 2.68 2.68 2.67 2.67 ±10 −40°C ≤ TA ≤ +125°C Output Current IO −40°C ≤ TA ≤ +125°C POWER SUPPLY Power Supply Rejection Ratio Supply Current/Amplifier INPUT CAPACITANCE Differential Common-Mode DYNAMIC PERFORMANCE Slew Rate Overload Recovery Time Gain Bandwidth Product NOISE PERFORMANCE Voltage Noise Voltage Noise Density Current Noise Density PSRR ISY VS = 2.7 V to 5.5 V −40°C ≤ TA ≤ +125°C VO = 0 V −40°C ≤ TA ≤ +125°C CIN SR 2.695 2.695 2.68 2.675 1 2 10 15 ±15 ±10 ±10 ±5 130 0.75 0.9 0.02 5 5 20 20 1.0 1.2 V V V V mV mV mV mV mA mA mA mA dB mA mA 1.5 10 pF pF RL = 10 kΩ 1 0.05 2 V/µs ms MHz 0.1 Hz to 10 Hz f = 1 kHz f = 10 Hz 0.5 22 5 µV p-p nV/√Hz fA/√Hz GBP en p-p en in 115 130 120 140 130 0.002 Rev. C | Page 4 of 20 AD8628/AD8629 ABSOLUTE MAXIMUM RATINGS Table 3. Parameters Supply Voltage Input Voltage Differential Input Voltage1 Output Short-Circuit Duration to GND Storage Temperature Range R, RM, RT, UJ Packages Operating Temperature Range Junction Temperature Range R, RM, RT, UJ Packages Lead Temperature Range (Soldering, 60 s) 1 Ratings 6V GND − 0.3 V to VS− + 0.3 V ±5.0 V Indefinite Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. −65°C to +150°C −40°C to +125°C Table 4. Thermal Characteristics Package Type 5-Lead TSOT-23 (UJ-5) 5-Lead SOT-23 (RT-5) 8-Lead SOIC (R-8) 8-Lead MSOP (RM-8) −65°C to +150°C 300°C Differential input voltage is limited to ±5 V or the supply voltage, whichever is less. 1 θJA1 207 230 158 190 θJC 61 146 43 44 Unit °C/W °C/W °C/W °C/W θJA is specified for worst-case conditions, that is, θJA is specified for the device soldered in a circuit board for surface-mount packages. ESD CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. Rev. C | Page 5 of 20 AD8628/AD8629 TYPICAL PERFORMANCE CHARACTERISTICS 180 100 VS = 2.7V TA = 25°C VS = 5V VCM = 2.5V TA = 25°C 90 80 140 NUMBER OF AMPLIFIERS 120 100 80 60 40 70 60 50 40 30 20 0 –2.5 –1.5 –0.5 0.5 INPUT OFFSET VOLTAGE (µV) 1.5 10 0 –2.5 2.5 Figure 5. Input Offset Voltage Distribution at 2.7 V –1.5 1.5 2.5 7 +85°C NUMBER OF AMPLIFIERS 40 30 20 +25°C 10 0 1 2 3 4 5 INPUT COMMON-MODE VOLTAGE (V) 5 4 3 2 1 02735-004 –40°C 0 VS = 5V TA = –40°C TO +125°C 6 50 02735-007 VS = 5V 0 6 0 2 Figure 6. Input Bias Current vs. Input Common-Mode Voltage at 5 V 4 6 TCVOS (nV/°C) 8 10 1 10 Figure 9. Input Offset Voltage Drift 1500 1k VS = 5V VS = 5V TA = 25°C 150°C 1000 100 125°C OUTPUT VOLTAGE (mV) INPUT BIAS CURRENT (pA) –0.5 0.5 INPUT OFFSET VOLTAGE (µV) Figure 8. Input Offset Voltage Distribution at 5 V 60 INPUT BIAS CURRENT (pA) 02735-006 02735-003 20 500 0 –500 10 SOURCE SINK 1 0.1 02735-005 –1000 –1500 0 1 2 3 4 5 INPUT COMMON-MODE VOLTAGE (V) 0.01 0.0001 6 Figure 7. Input Bias Current vs. Input Common-Mode Voltage at 5 V 02735-008 NUMBER OF AMPLIFIERS 160 0.001 0.01 0.1 LOAD CURRENT (mA) Figure 10. Output Voltage to Supply Rail vs. Load Current at 5 V Rev. C | Page 6 of 20 AD8628/AD8629 1k 1000 TA = 25°C VS = 2.7V 800 SUPPLY CURRENT (µA) 10 SOURCE SINK 1 0.1 600 400 0.01 0.0001 0.001 0.01 0.1 LOAD CURRENT (mA) 1 02735-012 02735-009 200 0 10 0 Figure 11. Output Voltage to Supply Rail vs. Load Current at 2.7 V 02735-010 –25 0 25 50 75 100 TEMPERATURE (°C) 125 150 0 30 45 20 90 10 135 0 180 –10 225 –20 –30 10k 175 PHASE SHIFT (Degrees) 40 02735-013 OPEN-LOOP GAIN (dB) INPUT BIAS CURRENT (pA) 50 100 100k 1M FREQUENCY (Hz) 10M Figure 15. Open-Loop Gain and Phase vs. Frequency Figure 12. Input Bias Current vs. Temperature 70 1250 TA = 25°C VS = 5V CL = 20pF RL = ∞ φM = 52.1° 60 5V 50 2.7V 750 500 02735-011 250 0 50 100 TEMPERATURE (°C) 150 40 0 30 45 20 90 10 135 0 180 –10 225 02735-014 OPEN-LOOP GAIN (dB) 1000 SUPPLY CURRENT (µA) 6 VS = 2.7V CL = 20pF RL = ∞ φM = 52.1° 60 450 0 –50 5 70 VS = 5V VCM = 2.5V TA = –40°C TO +150°C 900 0 –50 2 3 4 SUPPLY VOLTAGE (V) Figure 14. Supply Current vs. Supply Voltage 1500 1150 1 –20 –30 10k 200 Figure 13. Supply Current vs. Temperature 100k 1M FREQUENCY (Hz) 10M Figure 16. Open-Loop Gain and Phase vs. Frequency Rev. C | Page 7 of 20 PHASE SHIFT (Degrees) OUTPUT VOLTAGE (mV) 100 AD8628/AD8629 70 300 VS = 2.7V CL = 20pF RL = 2kΩ 60 VS = 5V 270 240 OUTPUT IMPEDANCE (Ω) 40 AV = 100 30 20 AV = 10 10 0 AV = 1 AV = 100 150 120 90 AV = 10 60 –20 –30 1k AV = 1 180 02735-015 –10 210 10k 100k 1M FREQUENCY (Hz) 02735-018 CLOSED-LOOP GAIN (dB) 50 30 0 100 10M Figure 17. Closed-Loop Gain vs. Frequency at 2.7 V 1k 10k 100k 1M FREQUENCY (Hz) 10M 100M Figure 20. Output Impedance vs. Frequency at 5 V 70 VS = 5V CL = 20pF RL = 2kΩ 60 AV = 100 40 VOLTAGE (500mV/DIV) CLOSED-LOOP GAIN (dB) 50 30 AV = 10 20 10 AV = 1 0 VS = ±1.35V CL = 300pF RL = ∞ AV = 1 02735-016 02735-019 –10 –20 –30 1k 10k 100k 1M FREQUENCY (Hz) 10M TIME (4µs/DIV) Figure 21. Large Signal Transient Response at 2.7 V Figure 18. Closed-Loop Gain vs. Frequency at 5 V 300 VS = 2.7V 270 VOLTAGE (1V/DIV) AV = 1 210 180 AV = 100 150 120 VS = ±2.5V CL = 300pF RL = ∞ AV = 1 90 30 0 100 02735-020 AV = 10 60 02735-017 OUTPUT IMPEDANCE (Ω) 240 1k 10k 100k 1M FREQUENCY (Hz) 10M 100M TIME (5µs/DIV) Figure 22. Large Signal Transient Response at 5 V Figure 19. Output Impedance vs. Frequency at 2.7 V Rev. C | Page 8 of 20 AD8628/AD8629 80 VS = ±1.35V CL = 50pF RL = ∞ AV = 1 VS = ±2.5V RL = 2kΩ TA = 25°C 70 OVERSHOOT (%) VOLTAGE (50mV/DIV) 60 50 40 30 OS– 20 02735-021 OS+ 02735-024 10 0 1 TIME (4µs/DIV) Figure 23. Small Signal Transient Response at 2.7 V 10 100 CAPACITIVE LOAD (pF) 1k Figure 26. Small Signal Overshoot vs. Load Capacitance at 5 V VS = ±2.5V CL = 50pF RL = ∞ AV = 1 VS = ±2.5V AV = –50 RL = 10kΩ CL = 0 CH1 = 50mV/DIV CH2 = 1V/DIV 0V 0V 02735-025 02735-022 VOLTAGE (V) VOLTAGE (50mV/DIV) VIN VOUT TIME (4µs/DIV) TIME (2µs/DIV) Figure 27. Positive Overvoltage Recovery Figure 24. Small Signal Transient Response at 5 V 100 VS = ±1.35V RL = 2kΩ TA = 25°C 90 0V VS = ±2.5V AV = –50 RL = 10kΩ CL = 0 CH1 = 50mV/DIV CH2 = 1V/DIV 80 VOLTAGE (V) 60 OS– 50 40 VIN VOUT OS+ 30 20 10 0 1 10 100 CAPACITIVE LOAD (pF) 1k 02735-026 0V 02735-023 OVERSHOOT (%) 70 TIME (10µs/DIV) Figure 28. Negative Overvoltage Recovery Figure 25. Small Signal Overshoot vs. Load Capacitance at 2.7 V Rev. C | Page 9 of 20 AD8628/AD8629 140 VS = ±2.5V VIN = 1kHz @ ±3V p-p CL = 0pF RL = 10kΩ AV = 1 VS = ±1.35V 120 100 PSRR (dB) VOLTAGE (1V/DIV) 80 60 +PSRR 40 20 –PSRR 0 –40 –60 100 TIME (200µs/DIV) 140 120 100 100 80 80 60 60 PSRR (dB) 120 40 20 –20 –40 1M 10M –PSRR –40 –60 100 10M 1k 10k 100k FREQUENCY (Hz) Figure 33. PSRR vs. Frequency Figure 30. CMRR vs. Frequency at 2.7 V 3.0 140 VS = 5V VS = 2.7V RL = 10kΩ TA = 25°C AV = 1 2.5 OUTPUT SWING (V p-p) 100 80 60 40 20 0 –20 2.0 1.5 1.0 –40 1k 10k 100k FREQUENCY (Hz) 1M 0 100 10M 02735-032 0.5 02735-029 CMRR (dB) 1M VS = ±2.5V 20 –20 –60 100 10M +PSRR 0 120 1M 40 0 02735-028 CMRR (dB) VS = 2.7V 10k 100k FREQUENCY (Hz) 10k 100k FREQUENCY (Hz) 02735-031 140 1k 1k Figure 32. PSRR vs. Frequency Figure 29. No Phase Reversal –60 100 02735-030 02735-027 –20 1k 10k FREQUENCY (Hz) 100k Figure 34. Maximum Output Swing vs. Frequency Figure 31. CMRR vs. Frequency at 5 V Rev. C | Page 10 of 20 1M AD8628/AD8629 5.5 120 VS = 2.7V NOISE AT 1kHz = 21.3nV 5.0 4.0 3.5 3.0 2.5 2.0 1.5 0.5 0 100 1k 10k FREQUENCY (Hz) 100k 90 75 60 45 30 15 02735-033 1.0 105 02735-036 OUTPUT SWING (V p-p) 4.5 VOLTAGE NOISE DENSITY (nV/√Hz) VS = 5V RL = 10kΩ TA = 25°C AV = 1 0 1M 0 Figure 35. Maximum Output Swing vs. Frequency at 5 V 2.0 2.5 120 VS = 2.7V VOLTAGE NOISE DENSITY (nV/√Hz) 0.30 0.15 0 –0.15 –0.30 –0.60 0 1 2 3 4 5 6 TIME (µs) 7 8 9 90 75 60 45 30 15 02735-034 –0.45 VS = 2.7V NOISE AT 10kHz = 42.4nV 105 02735-037 0.45 VOLTAGE (µV) 1.0 1.5 FREQUENCY (kHz) Figure 38. Voltage Noise Density at 2.7 V from 0 Hz to 2.5 kHz 0.60 0 10 0 Figure 36. 0.1 Hz to 10 Hz Noise at 2.7 V 5 10 15 FREQUENCY (kHz) 20 25 Figure 39. Voltage Noise Density at 2.7 V from 0 Hz to 25 kHz 0.60 120 VS = 5V VOLTAGE NOISE DENSITY (nV/√Hz) 0.30 0.15 0 –0.15 –0.30 –0.60 0 1 2 3 4 5 6 TIME (µs) 7 8 9 90 75 60 45 30 15 02735-035 –0.45 VS = 5V NOISE AT 1kHz = 22.1nV 105 02735-038 0.45 VOLTAGE (µV) 0.5 0 10 0 Figure 37. 0.1 Hz to 10 Hz Noise at 5 V 0.5 1.0 1.5 FREQUENCY (kHz) 2.0 Figure 40. Voltage Noise Density at 5 V from 0 Hz to 2.5 kHz Rev. C | Page 11 of 20 2.5 AD8628/AD8629 150 105 90 75 60 45 30 02735-039 15 0 0 5 10 15 FREQUENCY (kHz) 20 VS = 2.7V TA = –40°C TO +150°C 100 50 ISC– 0 ISC+ –50 –100 –50 25 Figure 41. Voltage Noise Density at 5 V from 0 Hz to 25 kHz –25 0 25 50 75 100 TEMPERATURE (°C) 125 150 175 Figure 44. Output Short-Circuit Current vs. Temperature 120 150 90 75 60 45 30 02735-040 15 0 0 5 FREQUENCY (kHz) VS = 5V TA = –40°C TO +150°C 100 ISC– 50 0 –50 ISC+ –100 –50 10 02735-043 105 OUTPUT SHORT-CIRCUIT CURRENT (mA) VS = 5V VOLTAGE NOISE DENSITY (nV/√Hz) 02735-042 VS = 5V NOISE AT 10kHz = 36.4nV OUTPUT SHORT-CIRCUIT CURRENT (mA) VOLTAGE NOISE DENSITY (nV/√Hz) 120 –25 0 25 50 75 100 TEMPERATURE (°C) 125 150 175 Figure 45. Output Short-Circuit Current vs. Temperature Figure 42. Voltage Noise 1k 150 VS = 5V VS = 2.7V TO 5V TA = –40°C TO +125°C 120 110 100 90 80 70 60 50 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 VCC – VOH @ 1kΩ 100 VOL – VEE @ 1kΩ VCC – VOH @ 10kΩ 10 VOL – VEE @ 10kΩ VCC – VOH @ 100kΩ 1 VOL – VEE @ 100kΩ 0.10 –50 125 Figure 43. Power Supply Rejection vs. Temperature 02735-044 OUTPUT-TO-RAIL VOLTAGE (mV) 130 02735-041 POWER SUPPLY REJECTION (dB) 140 –25 0 25 50 75 100 TEMPERATURE (°C) 125 150 Figure 46. Output-to-Rail Voltage vs. Temperature Rev. C | Page 12 of 20 175 AD8628/AD8629 140 1k VSY = ±2.5V 120 VOL – VEE @ 1kΩ VCC – VOH @ 10kΩ 10 VCC – VOH @ 100kΩ 1 VOL – VEE @ 10kΩ VOL – VEE @ 100kΩ 0.10 –50 –25 0 25 50 75 100 TEMPERATURE (°C) 125 150 100 80 60 40 R1 10kΩ +2.5V VIN 28mV p-p + – 20 R2 100Ω V– V+ A B V– VOUT V+ 02735-062 CHANNEL SEPARATION (dB) VCC – VOH @ 1kΩ 100 02735-045 OUTPUT-TO-RAIL VOLTAGE (mV) VS = 2.7V –2.5V 0 1k 175 10k 100k FREQUENCY (Hz) 1M Figure 48. AD8629 Channel Separation Figure 47. Output-to-Rail Voltage vs. Temperature Rev. C | Page 13 of 20 10M AD8628/AD8629 FUNCTIONAL DESCRIPTION The AD8628/AD8629 are single-supply, ultrahigh precision rail-to-rail input and output operational amplifiers. The typical offset voltage of less than 1 µV allows these amplifiers to be easily configured for high gains without risk of excessive output voltage errors. The extremely small temperature drift of 2 nV/°C ensures a minimum of offset voltage error over their entire temperature range of −40°C to +125°C, making these amplifiers ideal for a variety of sensitive measurement applications in harsh operating environments. 1/F NOISE The AD8628/AD8629 achieve a high degree of precision through a patented combination of auto-zeroing and chopping. This unique topology allows the AD8628/AD8629 to maintain their low offset voltage over a wide temperature range and over their operating lifetime. The AD8628/AD8629 also optimize the noise and bandwidth over previous generations of auto-zero amplifiers, offering the lowest voltage noise of any auto-zero amplifier by more than 50%. The internal elimination of 1/f noise is accomplished as follows. 1/f noise appears as a slowly varying offset to AD8628/AD8629 inputs. Auto-zeroing corrects any dc or low frequency offset. Therefore, the 1/f noise component is essentially removed, leaving the AD8628/AD8629 free of 1/f noise. 120 Rev. C | Page 14 of 20 LTC2050 (89.7nV/√Hz) 105 90 75 60 LMC2001 (31.1nV/√Hz) 45 30 15 AD8628 (19.4nV/√Hz) MK AT 1kHz FOR ALL 3 GRAPHS 0 0 2 4 6 FREQUENCY (kHz) 8 10 Figure 49. Noise Spectral Density of AD8628 vs. Competition 02735-046 The AD8628 is among the few auto-zero amplifiers offered in the 5-lead TSOT-23 package. This provides a significant improvement over the ac parameters of the previous auto-zero amplifiers. The AD8628/AD8629 have low noise over a relatively wide bandwidth (0 Hz to 10 kHz) and can be used where the highest dc precision is required. In systems with signal bandwidths of from 5 kHz to 10 kHz, the AD8628/ AD8629 provide true 16-bit accuracy, making them the best choice for very high resolution systems. One of the biggest advantages that the AD8628/AD8629 bring to systems applications over competitive auto-zero amplifiers is their very low noise. The comparison shown in Figure 49 indicates an input-referred noise density of 19.4 nV/√Hz at 1 kHz for the AD8628, which is much better than the LTC2050 and LMC2001. The noise is flat from dc to 1.5 kHz, slowly increasing up to 20 kHz. The lower noise at low frequency is desirable where auto-zero amplifiers are widely used. VOLTAGE NOISE DENSITY (nV/√Hz) Previous designs used either auto-zeroing or chopping to add precision to the specifications of an amplifier. Auto-zeroing results in low noise energy at the auto-zeroing frequency, at the expense of higher low-frequency noise due to aliasing of wideband noise into the auto-zeroed frequency band. Chopping results in lower low-frequency noise at the expense of larger noise energy at the chopping frequency. The AD8628/AD8629 family use both auto-zeroing and chopping in a patented pingpong arrangement to obtain lower low-frequency noise together with lower energy at the chopping and auto-zeroing frequencies, maximizing the signal-to-noise ratio (SNR) for the majority of applications without the need for additional filtering. The relatively high clock frequency of 15 kHz simplifies filter requirements for a wide, useful, noise-free bandwidth. 1/f noise, also known as pink noise, is a major contributor to errors in dc-coupled measurements. This 1/f noise error term can be in the range of several µV or more, and, when amplified with the closed-loop gain of the circuit, can show up as a large output offset. For example, when an amplifier with a 5 µV p-p 1/f noise is configured for a gain of 1,000, its output has 5 mV of error due to the 1/f noise. But the AD8628/AD8629 eliminate 1/f noise internally, and thereby greatly reduce output errors. 12 AD8628/AD8629 50 PEAK-TO-PEAK NOISE 45 Because of the ping-pong action between auto-zeroing and chopping, the peak-to-peak noise of the AD8628/AD8629 is much lower than the competition. Figure 50 and Figure 51 show this comparison. 40 NOISE (dB) 35 en p-p = 0.5µV BW = 0.1Hz TO 10Hz 30 25 20 VOLTAGE (0.5µV/DIV) 15 02735-050 10 5 0 0 10 20 30 40 50 60 FREQUENCY (Hz) 70 80 90 100 Figure 53. Simulation Transfer Function of the Test Circuit 02735-047 50 45 40 TIME (1s/DIV) 35 NOISE (dB) Figure 50. AD8628 Peak-to-Peak Noise en p-p = 2.3µV BW = 0.1Hz TO 10Hz 30 25 20 15 02735-051 VOLTAGE (0.5µV/DIV) 10 5 0 0 10 20 30 40 50 60 70 FREQUENCY (kHz) 80 90 100 Figure 54. Actual Transfer Function of Test Circuit 02735-048 The measured noise spectrum of the test circuit shows that noise between 5 kHz and 45 kHz is successfully rolled off by the first-order filter. TOTAL INTEGRATED INPUT-REFERRED NOISE FOR FIRST-ORDER FILTER Figure 51. LTC2050 Peak-to-Peak Noise NOISE BEHAVIOR WITH FIRST-ORDER LOW-PASS FILTER The AD8628 was simulated as a low-pass filter and then configured as shown in Figure 52. The behavior of the AD8628 matches the simulated data. It was verified that noise is rolled off by first-order filtering. IN OUT LTC2050 AD8551 Figure 52. Test Circuit: First-Order Low-Pass Filter—×101 Gain and 3 kHz Corner Frequency 0.1 10 100 1k 3dB FILTER BANDWIDTH (Hz) Figure 55. 3 dB Filter Bandwidth in Hz Rev. C | Page 15 of 20 AD8628 1 02735-052 1kΩ 470pF 10 02735-049 100kΩ For a first-order filter, the total integrated noise from the AD8628 is lower than the LTC2050. RMS NOISE (µV) TIME (1s/DIV) 10k AD8628/AD8629 INPUT OVERVOLTAGE PROTECTION These diodes are connected between the inputs and each supply rail to protect the input transistors against an electrostatic discharge event and are normally reverse-biased. However, if the input voltage exceeds the supply voltage, these ESD diodes can become forward-biased. Without current limiting, excessive amounts of current could flow through these diodes, causing permanent damage to the device. If inputs are subject to overvoltage, appropriate series resistors should be inserted to limit the diode current to less than 5 mA maximum. 0V 0V 02735-053 VOLTAGE (V) Although the AD8628/AD8629 are rail-to-rail input amplifiers, care should be taken to ensure that the potential difference between the inputs does not exceed the supply voltage. Under normal negative feedback operating conditions, the amplifier corrects its output to ensure that the two inputs are at the same voltage. However, if either input exceeds either supply rail by more than 0.3 V, large currents begin to flow through the ESD protection diodes in the amplifier. CH1 = 50mV/DIV CH2 = 1V/DIV AV = –50 VIN VOUT TIME (500µs/DIV) Figure 56. Positive Input Overload Recovery for the AD8628 CH1 = 50mV/DIV CH2 = 1V/DIV AV = –50 VIN 0V 0V 02735-054 Output phase reversal occurs in some amplifiers when the input common-mode voltage range is exceeded. As common-mode voltage is moved outside of the common-mode range, the outputs of these amplifiers can suddenly jump in the opposite direction to the supply rail. This is the result of the differential input pair shutting down, causing a radical shifting of internal voltages that results in the erratic output behavior. VOLTAGE (V) OUTPUT PHASE REVERSAL VOUT The AD8628/AD8629 amplifiers have been carefully designed to prevent any output phase reversal, provided that both inputs are maintained within the supply voltages. If one or both inputs could exceed either supply voltage, a resistor should be placed in series with the input to limit the current to less than 5 mA. This ensures that the output does not reverse its phase. TIME (500µs/DIV) Figure 57. Positive Input Overload Recovery for LTC2050 CH1 = 50mV/DIV CH2 = 1V/DIV AV = –50 VIN Rev. C | Page 16 of 20 0V 0V 02735-055 Many auto-zero amplifiers are plagued by a long overload recovery time, often in ms, due to the complicated settling behavior of the internal nulling loops after saturation of the outputs. The AD8628/AD8629 have been designed so that internal settling occurs within two clock cycles after output saturation happens. This results in a much shorter recovery time, less than 10 µs, when compared to other auto-zero amplifiers. The wide bandwidth of the AD8628/AD8629 enhances performance when they are used to drive loads that inject transients into the outputs. This is a common situation when an amplifier is used to drive the input of switched capacitor ADCs. VOLTAGE (V) OVERLOAD RECOVERY TIME VOUT TIME (500µs/DIV) Figure 58. Positive Input Overload Recovery for LMC2001 AD8628/AD8629 The results shown in Figure 56 to Figure 61 are summarized in Table 5. 0V VOLTAGE (V) CH1 = 50mV/DIV CH2 = 1V/DIV AV = –50 Table 5. Overload Recovery Time VIN VOUT 02735-056 0V Negative Overload Recovery (µs) 9 25,000 35,000 INFRARED SENSORS Infrared (IR) sensors, particularly thermopiles, are increasingly being used in temperature measurement for applications as wide-ranging as automotive climate control, human ear thermometers, home insulation analysis, and automotive repair diagnostics. The relatively small output signal of the sensor demands high gain with very low offset voltage and drift to avoid dc errors. TIME (500µs/DIV) Figure 59. Negative Input Overload Recovery for the AD8628 0V CH1 = 50mV/DIV CH2 = 1V/DIV AV = –50 VIN VOUT 0V 02735-057 VOLTAGE (V) Positive Overload Recovery (µs) 6 650 40,000 Product AD8628 LTC2050 LMC2001 If interstage ac coupling is used (Figure 62), low offset and drift prevents the input amplifier’s output from drifting close to saturation. The low input bias currents generate minimal errors from the sensor’s output impedance. As with pressure sensors, the very low amplifier drift with time and temperature eliminates additional errors once the temperature measurement has been calibrated. The low 1/f noise improves SNR for dc measurements taken over periods often exceeding 1/5 s. Figure 64 (shows a circuit that can amplify ac signals from 100 µV to 300 µV up to the 1 V to 3 V level, with gain of 10,000 for accurate A/D conversion. TIME (500µs/DIV) Figure 60. Negative Input Overload Recovery for LTC2050 10kΩ 100Ω 100kΩ 100kΩ 5V 5V 100µV – 300µV IR DETECTOR VIN VOUT 10µF 1/2 AD8629 1/2 AD8629 10kΩ fC ≈ 1.6Hz TO BIAS VOLTAGE Figure 62. AD8629 Used as Preamplifier for Thermopile 0V 02735-058 VOLTAGE (V) CH1 = 50mV/DIV CH2 = 1V/DIV AV = –50 TIME (500µs/DIV) Figure 61. Negative Input Overload Recovery for LMC2001 Rev. C | Page 17 of 20 02735-059 0V AD8628/AD8629 PRECISION CURRENT SHUNTS OUTPUT AMPLIFIER FOR HIGH PRECISION DACs A precision shunt current sensor benefits from the unique attributes of auto-zero amplifiers when used in a differencing configuration (Figure 63). Shunt current sensors are used in precision current sources for feedback control systems. They are also used in a variety of other applications, including battery fuel gauging, laser diode power measurement and control, torque feedback controls in electric power steering, and precision power metering. The AD8628/AD8629 are used as output amplifiers for a 16-bit high precision DAC in a unipolar configuration. In this case, the selected op amp needs to have very low offset voltage (the DAC LSB is 38 µV when operated with a 2.5 V reference) to eliminate the need for output offset trims. Input bias current (typically a few tens of picoamperes) must also be very low, because it generates an additional zero code error when multiplied by the DAC output impedance (approximately 6 kΩ). SUPPLY I 100kΩ e = 1,000 RS I 100mV/mA RS 0.1Ω Rail-to-rail input and output provide full-scale output with very little error. Output impedance of the DAC is constant and codeindependent, but the high input impedance of the AD8628/ AD8629 minimizes gain errors. The amplifiers’ wide bandwidth also serves well in this case. The amplifiers, with settling time of 1 µs, add another time constant to the system, increasing the settling time of the output. The settling time of the AD5541 is 1 µs. The combined settling time is approximately 1.4 µs, as can be derived from the following equation: RL 100Ω C 5V AD8628 100Ω C 02735-060 100kΩ t S (TOTAL ) = (t S DAC )2 + (t S AD8628 )2 Figure 63. Low-Side Current Sensing 5V 2.5V 0.1µF 0.1µF SERIAL INTERFACE Rev. C | Page 18 of 20 VDD 10µF REF(REF*) REFS* CS DIN SCLK AD5541/AD5542 LDAC* UNIPOLAR OUTPUT OUT AD8628 DGND AGND *AD5542 ONLY Figure 64. AD8628 Used as an Output Amplifier 03023-061 In such applications, it is desirable to use a shunt with very low resistance to minimize the series voltage drop; this minimizes wasted power and allows the measurement of high currents without saving power. A typical shunt might be 0.1 Ω. At measured current values of 1 A, the shunt’s output signal is hundreds of mV, or even V, and amplifier error sources are not critical. However, at low measured current values in the 1 mA range, the 100 µV output voltage of the shunt demands a very low offset voltage and drift to maintain absolute accuracy. Low input bias currents are also needed, so that injected bias current does not become a significant percentage of the measured current. High open-loop gain, CMRR, and PSRR all help to maintain the overall circuit accuracy. As long as the rate of change of the current is not too fast, an auto-zero amplifier can be used with excellent results. AD8628/AD8629 OUTLINE DIMENSIONS 2.90 BSC 5 5.00 (0.1968) 4.80 (0.1890) 4 2.80 BSC 1.60 BSC 8 1 2 5 4.00 (0.1574) 3.80 (0.1497) 1 3 6.20 (0.2440) 4 5.80 (0.2284) PIN 1 0.95 BSC 1.27 (0.0500) BSC 1.90 BSC 0.90 0.87 0.84 0.25 (0.0098) 0.10 (0.0040) 1.00 MAX 0.10 MAX 0.50 0.30 8° 4° SEATING PLANE 0.20 0.08 0.51 (0.0201) COPLANARITY SEATING 0.31 (0.0122) 0.10 PLANE 0.60 0.45 0.30 0.50 (0.0196) × 45° 0.25 (0.0099) 1.75 (0.0688) 1.35 (0.0532) 8° 0.25 (0.0098) 0° 1.27 (0.0500) 0.40 (0.0157) 0.17 (0.0067) COMPLIANT TO JEDEC STANDARDS MO-193AB COMPLIANT TO JEDEC STANDARDS MS-012AA CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN Figure 65. 5-Lead Thin Small Outline Transistor Package [TSOT] (UJ-5) Dimensions shown in millimeters Figure 67. 8-Lead Standard Small Outline Package [SOIC] Narrow Body (R-8) Dimensions shown in millimeters and (inches) 2.90 BSC 3.00 BSC 5 4 2.80 BSC 1.60 BSC 8 1 2 3 5 4.90 BSC 3.00 BSC PIN 1 4 0.95 BSC 1.90 BSC 1.30 1.15 0.90 PIN 1 0.65 BSC 1.45 MAX 0.15 MAX 0.50 0.30 SEATING PLANE 1.10 MAX 0.15 0.00 0.22 0.08 10° 5° 0° 0.60 0.45 0.30 0.38 0.22 COPLANARITY 0.10 0.23 0.08 8° 0° 0.80 0.60 0.40 SEATING PLANE COMPLIANT TO JEDEC STANDARDS MO-178AA COMPLIANT TO JEDEC STANDARDS MO-187AA Figure 66. 5-Lead Small Outline Transistor Package [SOT-23] (RT-5) Dimensions shown in millimeters Figure 65. 8-Lead Standard Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters Rev. C | Page 19 of 20 AD8628/AD8629 ORDERING GUIDE Model AD8628AUJ-R2 AD8628AUJ-REEL AD8628AUJ-REEL7 AD8628AUJZ-R21 AD8628AUJZ-REEL1 AD8628AUJZ-REEL71 AD8628AR AD8628AR-REEL AD8628AR-REEL7 AD8628ARZ1 AD8628ARZ-REEL1 AD8628ARZ-REEL71 AD8628ART-R2 AD8628ART-REEL7 AD8628ARTZ-R21 AD8628ARTZ-REEL71 AD8629ARZ1 AD8629ARZ-REEL1 AD8629ARZ-REEL71 AD8629ARMZ-R21 AD8629ARMZ-REEL1 1 Temperature Range −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C Package Description 5-Lead TSOT-23 5-Lead TSOT-23 5-Lead TSOT-23 5-Lead TSOT-23 5-Lead TSOT-23 5-Lead TSOT-23 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 5-Lead SOT-23 5-Lead SOT-23 5-Lead SOT-23 5-Lead SOT-23 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead MSOP 8-Lead MSOP Z = Pb-free part. © 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. C02735–0–10/04(C) Rev. C | Page 20 of 20 Package Option UJ-5 UJ-5 UJ-5 UJ-5 UJ-5 UJ-5 R-8 R-8 R-8 R-8 R-8 R-8 RT-5 RT-5 RT-5 RT-5 R-8 R-8 R-8 RM-8 RM-8 Branding AYB AYB AYB AYB AYB AYB AYA AYA AYA AYA A06 A06